Capacitive touch sensor devices have been incorporated into a variety of consumer electronics, including cellular telephones, computers, portable entertainment devices, appliances, and touch screens, to name a few. At a minimum, a capacitive touch sensor device includes one or more touch sensors (or “electrodes”), each of which is configured to indicate a capacitance change when the sensor is touched (e.g., by a stylus or a user's finger). Each sensor may be associated with a distinct user input, and the detection of a touch by a particular sensor may initiate a responsive process in the device. For example, to enable a user to make a telephone call, a cellular telephone with a relatively simple user interface may include an array of twelve sensors, with ten of the sensors being associated with each of the numbers from 0 to 9, an eleventh sensor being associated with a “SEND” key, and a twelfth sensor being associated with an “END” key. Each time the user touches a sensor associated with a number, the device displays the number and stores it in a register. When the register includes a set of numbers associated with a remote device (e.g., a telephone number), and the user touches a sensor associated with the “SEND” key, the device may initiate a connection with a communication network (e.g., a cellular telephone network). The device additionally may send to the network the set of numbers in the register, thus enabling the network to initiate a communication session with the remote device.
Some capacitive touch sensor devices also include a “proximity sensor” (or “proximity electrode”), which is distinct from the touch sensors, and which is configured to detect the approach or proximity of an object (e.g., a stylus or a user's finger) by sensing changes in capacitance, as opposed to detecting an actual touch. An indication by a proximity sensor that an object is approaching also may initiate a responsive process in the device. For example, when a proximity sensor indicates that an object is approaching, the device may cause a backlight to activate, thus illuminating a display screen. Such a feature may enable the device to conserve power, among other things, and proximity sensors have been used to initiate a variety of processes. A proximity sensor typically includes a relatively large, stand-alone electrode. Because of their size, proximity sensors typically are not included in devices that have crowded touch sensor arrays and/or severe size constraints.